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The Anatomy of the Hypodermic Needle and Syringe

26 Jul, 2021

The Anatomy of the Hypodermic Needle and Syringe

"You'll only feel a slight pinch," says the nurse as she drives the needle towards your skin. You see her place the needle into your skin and push the end of the device. Suddenly, it's all over.

If you've ever gone through an experience like this, you've likely come into contact with a hypodermic needle.

Medical professionals often use these needles to take blood samples, administer medications, give vaccines, and more. But, how does it actually work? What makes the hypodermic needles the ideal device to do these things?

If you're curious about this, keep reading. We're going to teach you all about what a hypodermic needle is, what the parts of the syringe are, and so much more.

What Is a Hypodermic Needle?

Some medical professionals refer to the hypodermic needle as the hypodermic syringe. These are both the same device.

The term 'hypodermic' comes from the combination of two words: hypo and derma. Both of these terms are Greek.

Hypo means 'under,' and derma means 'skin.' Together, this tells us that the term hypodermic means 'under the skin.'

This terminology is accurate and helpful as it describes exactly what it is meant to do. The needle/syringe is meant to go underneath the top layer of the skin.

Why Do Medical Professionals Use Hypodermic Needles?

This device is one of the primary ways to deliver medications to patients who need them. There are two other ways: oral delivery and transepidermal delivery.

However, there are significant advantages to the hypodermic approach.

First, the medication is able to bypass the digestive system. So, the stomach can't chemically alter or break down the medication.

Also, medications delivered under the skin reach the bloodstream faster. So, they can start worker faster.

Lastly, the body is less likely to reject medication that enters the body under the skin.

What Are the Parts of a Syringe?

The syringe part of this device has two or three parts. However, this doesn't include the needle that goes underneath the skin. Sometimes, these needles are already attached to the syringe while they're separate at other times.

A two-part medical syringe is most popular in Europe. In fact, the greater majority of the syringes that we see and use are two-part syringes. This kind of device has a plunger and a barrel.

The plunger is what creates the suction inside of the barrel. The barrel holds the liquid that medical professionals collect and/or administer. The plunger fits the needle perfectly to ensure that no liquid escapes the barrel.

When the plunger is in a down position, it releases the substance(s) inside of the barrel. When the plunger is in an up position, it sucks substance(s) into the barrel. Ideally, you're administering and gathering only the substance that you need.

A three-part syringe has a barrel and a plunger, too. But, it also has a cap. This is a rubber cap at the end of the plunger that lies inside of the barrel. This cap ensures that no liquid escapes the barrel by creating a tighter seal between the plunger and the barrel.

What About the Syringe Needle?

Now that you understand the syringe, it's time to attach the needle. There are two methods to do this correctly:

  1. Twist the needle into a Luer lock fitting
  2. Push the needle onto a Luer slip fitting

If the needle is already fixed into the syringe, you do not need to worry about performing either of these tactics. The device is ready to use.

However, if you do need to use one of these methods, you should understand the Luer lock and slip fittings.

Luer lock syringes have a thread that makes it easy to fit the needle via twisting. You should be sure to twist the needle enough to make a tight seal. Otherwise, liquid may escape the device.

Luer slip syringes are more common than Luer lock syringes. The Luer slip syringe features a taper that makes a leak-proof connection between the syringe and the needle.

In theory, all Luer slip syringes should be the same since there is an international standard for Luer tapers. This means that all needles should be able to flip into any Luer slip syringe.

To attach the needle, you just need to put the needle onto the syringe. Sometimes, you may need to use a small twisting motion to ensure that the needle is on the syringe tightly.

The taper holds onto the needle with friction. So, the seal remains good.

Because of this mechanism, some people refer to Luer slip syringes as Luer lock syringes.

Hypodermic Needle Sizes

The needle gauge of a hypodermic needle refers to the circumference or thickness of the needle. To measure this, professionals use the gauge system. So, the higher the number, the finer the needle is.

Injection needles can range from 32G to 16G.

Most recently, different gauges have been divided according to colour. Here are some examples of the colouring system:

  • 33G = Green
  • 32G = Pink
  • 31G = Light Blue
  • 30G = Yellow
  • 29G = Red
  • 28G = Blue-Green
  • 27G = Grey
  • 26G = Brown
  • 25G = Orange
  • 23G = Dark Blue
  • 22G = Black
  • 21G = Dark Green
  • 20G = Yellow
  • 19G = Cream
  • 18G = Pink
  • 16G = White

The diameter of each one of these needles is standardised via an ISO standard. So, each gauge should remain the same around the world, no matter where you go.

Hypodermic Needle Bore

The bore of the needle is the hole that goes down the centre of the needle. In general, larger needles have larger bores.

If small needles had bores that were too large, it could compromise the integrity of the needles. The outer walls would be thin and at risk for collapse.

What Are Hypodermic Needles Made With?

Because of government regulations and bodily needs, all hypodermic needles are made with biocompatible materials that are pharmacologically inert. On top of this, the syringes and needles must be sterilized and nontoxic.

All of these requirements are better for the patients as they make sure that they won't have unnecessary reactions to the needle or syringe.

Different kinds of syringes and needles are made with different materials. In general, each syringe and needle should have heat-treatable stainless steel or carbon steel. And, many have a nickel exterior to prevent corrosion.

The main tube is normally made of glass, plastic, or both. Plastic makes up the plunger and synthetic rubber makes up the plunger head.

All of these materials make it easy to clean the syringes and needles. Plus, they ensure that the human body is much less likely to produce a reaction.

How Do Manufacturers Ensure Needle Quality?

Because many of these hypodermic needles go to medical facilities, manufacturers need to make sure that they're of the utmost quality. Otherwise, liquids will leak and contamination will occur.

Parts of the hypodermic needle are made by the thousands. So, it's important to ensure that each part is up to the highest standards.

First, manufacturers will complete a primary inspection visually. Once this is done and good, they need to measure the equipment. This includes checking the length, width, and thickness of each piece.

As the manufacturers are making the materials, they're also checking for deformed parts, incorrect pieces, or wrong packaging.

Overall, these inspections ensure that each unit is meeting quality standards and government regulations. Additionally, the company may have its own regulations to keep in mind as they're making more units.

How Does a Hypodermic Needle Work?

Now that you understand the basic anatomy of a hypodermic needle, you need to understand how the needle functions. In fact, it's important to recognise the things that both syringes and needles perform within these devices.

If a medical professional is trying to take a sample and/or remove fluid, they will draw this substance up through the hollow needle on the end. The fluid will travel up the needle and into the main tube as the professional pulls back the plunger.

As long as the tip of the needle remains submerged in fluid, no air will enter the chamber. And, the person who is drawing the substance will be able to know when it's time to stop by looking at the measurements on the side of the tube. This will tell them how much of the substance they've collected.

If a medical professional is trying to administer a drug, vaccine, or something else, they'll insert the needle into the desired site. Then, they'll push the plunger down, pushing the substance out from the chamber and down the needle.

Buying Hypodermic Needles

Hypodermic needles are an essential piece of medical equipment for medical professionals and some chronic illness patients. And, if you're going to provide the best medical care, you need the best equipment.

So, we highly recommend that you check out our syringe and needle kits. With us, you can get our syringe and needle kits quickly and easily. So, you won't have to worry about running out if you're low on the supplies that you need.

Get started today and see the difference that quality medical equipment can make.